1. Field of the Invention
The present invention relates to a stabilizer bar used as a device for preventing rolling of vehicles such as passenger cars, trucks and the like.
2. Description of the Related Art
In general, vehicles such as passenger cars, trucks and the like have independent suspensions coupled with right and left wheels and a stabilizer is attached to the independent suspensions to prevent rolling of the vehicle. The stabilizer is formed of a steel tube material to reduce weight. Further, the stabilizer is three-dimensionally processed to prevent interference with various components disposed on a lower surface of a vehicle body such as differential gears, propeller shafts and the like.
Specifically, the stabilizer is formed in an approximate U-shape, uses its central linear portion as a torsion-bar spring (torsion unit), and forms arm portions by curving both sides of the central linear portion. An attachment portion, which is flattened by deformation processing, is formed at the free end of each arm portion extending from the respective curved portions. Through holes are formed in the attachment portions to attach the attachment portions to a vehicle body.
Recently, since the configuration of vehicle bodies has become more complex, the space available for attaching a stabilizer bar has been reduced. To cope with this problem, there have been demands to make the attachment portions, the width dimensions of which are increased by being flattened, more compact. Further, there have also been demands to bend the stabilizer at the positions of the attachment portions due to restrictions in attachment direction and the like.
Demands to make the attachment portions compact can be met by cutting and removing the parts of the attachment portions whose size in a width direction has been increased by flattening of the steel tube material by pressing and deforming the same.
Specifically, as shown in FIGS. 8A to 8E, in an attachment portion 80 (FIG. 8B), in which the free end of an arm 16 is pressed and deformed in the directions of arrows P1 (FIG. 8A) and which has a thickness T1 (about twice the wall thickness a of the pipe material) formed in a flat shape and a through hole 20 formed therein, the width dimension of the attachment portion 80, which has been increased to a width W1, can be reduced (FIG. 8C) by cutting and removing (trimming) the ends 80A of the attachment portion 80 along the positions of cutting lines 82 to a cut width W2 as a requested dimension.
However, in the trimming, since the inner peripheral surface 161 of the pipe material has been linearly extended, both the end portions of overlapping surfaces 84 having a length L1 (L1>W2) are cut off together with the ends 80A of the pipe material as shown in FIG. 8D (a cross section taken along S1-S1).
As a result, since the continuous property of the pipe material surrounding the overlapping surfaces 84 is lost as shown in FIG. 8E, the upper part 80U of the attachment portion 80 is separated from the lower part 80D thereof at the position of the overlapping surfaces 84.
When the attachment portion 80, in a state after it is trimmed as shown in FIG. 9A, is bent, a problem arises in that the through holes 20 are positionally offset from each other (FIG. 9B) and cannot be used because a radius of curvature of the upper part 80U of the pipe material is different from that of the lower part 80D thereof and thus demands for bending processing cannot be met.
Accordingly, a method of inserting solid materials into both end sides of the steel tube material and forming attachment portions by pressing and deforming the steel tube material together with the solid material has been proposed (Japanese Patent Application Laid-Open (JP-A) No. 2008-143313). However, the method of JP-A No. 2008-143313 increases costs.
In view of the above circumstances, an object of the invention is to provide a stabilizer bar in which through holes are not positionally offset from each other even if the stabilizer bar is bent after the through holes are formed at attachment portions.